Cathode ray tubes ("CRTs") are well known in modern society. The CRT is the principal component in such common devices as television and computer monitors. As shown in FIG. 1, a CRT (100) typically includes a relatively flat display portion (101) (upper portion as seen in FIG. 1). When one is watching television or looking at a computer monitor, that person is looking at the flat display portion (101) of a cathode ray tube.
During manufacture, an electro-luminescent material is coated over the display portion (101) of the CRT. The display portion (101) is then joined to the funnel (102) using a glass paste compound known as frit to complete the cathode ray tube shown, for example, in FIG. 1). An electron gun (106) is then placed at the end of the CRT's "neck" (102). When the CRT is operated, a yoke (not shown) creating an electromagnetic field causes the stream of electrons (105) emitted from the electron gun (106) to scan in lines across the surface of the display portion (101).
Where the stream of electrons (105) hits the electro-luminescent material, the electro-luminescent material emits light. Thus, by rapidly switching the electron stream (105) on and off, or by varying the power of the electron stream as it sweeps across the display portion of the CRT, an image can be formed in the light emitted by the electro-luminescent material. This is the general principle on which CRTs operate.
After the display portion (101) of the tube is joined to the funnel (102) and the joint between the two is sealed with frit, the completed tube is evacuated. Then, the strength of the frit seal and the integrity of the vacuum are evaluated. This evaluation is known as "frit knocking" and is performed with a high voltage being applied from within the cathode ray tube (100).
Unfortunately, it is not uncommon for the high voltage (105) to arc (107) out of the neck (102) of the CRT (100) and into the support fixture (120). This may result in a puncture of the CRT neck (102) at the point where the arcing (107) occurred. This degrades the quality of the CRT or renders it unusable.
Consequently, there is a need in the art for a device and method that prevents the arcing of the high voltage so as to avoid punctures in the neck of the CRT during the frit knocking, i.e., the evaluation of the frit integrity.